Just looked at the map and found that I didn't actually miss out the big hill. Which I'm pleased about !!! Here are the details for those that are interested.
Using the 1:25 000 OS map number 151 (Stratford-upon-Avon) I can now see that I ran up Ebrington Hill from Chipping Campden (GR 165 396 to GR 188 427). However I took the right hand fork instead of the left about 450m from the summit (GR 187 422) - after running uphill for almost 4 km.
I rejoined the proper route immediately after the village of Ilmington (GR 214 440) and did indeed run only about half a mile short.